The invention relates to a tire, intended to bear heavy loads and be inflated to very high pressure, greater than 12 bar, such as for example an aircraft tire.
A tire which meets the above criteria has been used for a long time is composed of a radial carcass reinforcement, formed of one or more plies of textile reinforcement elements, which plies are generally divided into two groups: a first group, referred to as axially inner plies, which are anchored within each bead to at least one bead wire by winding around said bead wire, from the inside to the outside to form ply upturns; and a second group referred to as axially outer plies, the radially inner ends of which are generally arranged within each bead beneath the bead wire. Said radial carcass reinforcement is radially surmounted by a crown reinforcement formed of a plurality of layers of textile reinforcement elements which are inclined relative to the circumferential direction by a certain angle xcex1. So as to avoid the free ends of crown plies, said layers are obtained by winding, around a form, whether cylindrical or rounded, or a carcass reinforcement blank, a strip of at least one textile reinforcement element from one edge of the layer to the other, forming the desired angle with the equatorial plane.
The textile elements commonly used are of aliphatic polyamide, and have relatively poor tensile strength characteristics, which is why numerous plies are used. As for numerous tires, the use of aromatic polyamide or other similar material as material for reinforcing the crown reinforcement may prove advantageous in an aircraft tire, owing to the properties of said material. However, it is not easy to use such a material, and its use has numerous problems. For example, it is virtually impossible to use it in a crown reinforcement such as described above, obtained by winding a strip in a zigzag: the curvatures adopted by the strip, and hence by the reinforcement elements at the edge of the layer, impart to said elements very major tensions and compressions which, combined with the fact that the aromatic polyamide has resistances to said stresses which deteriorate with temperature, cancel out all the advantages of the aromatic polyamide.
A crown reinforcement, with plies, the edges of which are folded over on themselves, is also scarcely conceivable owing to the curvatures and adhesion to the rubber which is inferior to that of an aliphatic polyamide.
The object of the invention is to permit the use of aromatic polyamide as material for the main reinforcement elements of a crown reinforcement, by adapting the architecture of said reinforcement to the material.
The aircraft tire according to the invention, comprising a radial carcass reinforcement surmounted radially to the outside by a crown reinforcement and a tread, is characterized in that said crown reinforcement is composed:
a) of at least one ply of textile reinforcement elements oriented circumferentially, the secant modulus of extension of an element being at least equal to 200 cN/tex
b) of at least two plies having ends free of textile reinforcement elements, which are parallel to each other within each ply and are crossed from one ply to the next, forming with the circumferential direction an angle xcex1, of between 5xc2x0 and 35xc2x0, the secant modulus of extension of an element being at least equal to 200 cN/tex, and
c) radially to the outside, of at least two layers of textile reinforcement elements oriented relative to the circumferential direction at an angle xcex2, of between 0xc2x0 and 35xc2x0, the secant modulus of extension of an element being at most equal to 200 cN/tex, and said two layers being obtained by winding a strip, formed of at least one element coated with rubber mix, from one edge of said layers to the other, the assembly of said layers having an axial width greater than the tread width, whereas the widths of the plies formed of textile elements of high modulus are less than said tread width.
xe2x80x9cWidth of the treadxe2x80x9d is to be understood to mean the width, measured in the radial plane of the axis of the fitted wheel, of the contact surface between the tire mounted on its operating rim, inflated to the recommended pressure and bearing its standardised load.
xe2x80x9cCircumferentially oriented elementsxe2x80x9d is to be understood to mean elements forming with the circumferential direction angles which may be between 0xc2x0 and 10xc2x0.
The secant modulus of extension Ma of a reinforcement element is calculated for the assemblies in accordance with the equation:
Ma=F/xcex5.1/Ti
with F: force to which the assembly is subjected for a relative elongation of 4%,
xcex5: the relative elongation, equal to 4%,
Ti: linear density, expressed in Tex, of the assembly.
An element having a secant modulus greater than 200 cN/tex is referred to as an element of high modulus.
Preferably, the ply (plies) of circumferential elements is (are) directly located on the carcass reinforcement, and is (are) obtained by helical winding of a strip formed of at least one reinforcement element of aromatic polyamide, said element being coated with suitable rubber mix.
The plies formed of elements oriented at the angle xcex1, radially above the ply (plies) of circumferential elements, are also preferably formed of cables of aromatic polyamide and have axial widths which differ from each other but which are greater than the width(s) of said plies of circumferential elements while remaining less than the width of the tread.
All of the layers of the textile elements, having a modulus at most equal to 200 cN/tex, may be formed of cables of aliphatic polyamide, which are oriented relative to the circumferential direction at an angle xcex2, or of what are called hybrid cables, for example cables formed of two cords of aromatic polyamide and one cord of aliphatic polyamide, oriented in the same manner. Said assembly will preferably have an axial width such that the edges of said assembly are coupled to the carcass reinforcement over a developed width at least equal to 10% of said axial width. xe2x80x9cEdge coupled to the carcass reinforcementxe2x80x9d is to be understood to mean an edge in contact over a certain length with said reinforcement and separated from said reinforcement by a thickness of rubber equal to the total of the greater and lesser thicknesses respectively of the calendering layers of the final carcass reinforcement ply and the layer of the assembly in contact with said final ply. The above variant permits a distinct improvement in the endurance of the crown reinforcement from the point of view of inter-ply separations, and also higher speed, while permitting an increase in the bursting pressure of the tire, as well as better uniformity of said tire, in particular from the cyclic point of view, which minimizes abnormal tread wear.
As is known per se, and although in the case of small dimensions the assembly of the layers of the reinforcement elements of a modulus at most equal to 200 cN/tex may advantageously play the role of protective layers, the crown reinforcement thus claimed will be advantageously finished off by at least one protective ply formed of metallic elements which undulate in the plane of the ply, said ply being located radially to the outside of the assembly of the layers of cables of aliphatic polyamide.
The invention will be more fully understood with reference to the accompanying drawings.